Genotype X Environment Interactions in Sheep
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AN ABSTRACT OF THE THESIS OF KATHLEEN STEELE CORUM for the degree MASTER OF SCIENCE (Name of student) (Degree) in ANIMAL BREEDING AND GENETICS presented on/ (Major department) (Date Title: GENOTYPE X ENVIRONMENT INTERACTIONS IN SHEEP Abstract approved: Redacted for privacy (Signature) William D. Hohenboken The 865 ewe production records taken from three lamb crops, were analyzed to study breed effects, heterosis, environmental effects and interactions between them, and breed and heterosis x environment inter- action effects on ewe production traits. In each of two environments, approximately 144 ewes were mated in a three breed reciprocal cross design each year. The resulting 757 parturitions produced 1263 lambs. Hampshire, Suffolk and Willamette sheep from university flocks were used. Two rams of each breed were used in each environment each year. One location was rolling hill land, the other was level, irrigated, valley bottom land, both near Corvallis, Oregon. Least squares analyses of variance were computed on ewe production traits which included fertility, lambs born, percent survival to weaning, lambs weaned and pounds of lamb weaned. None of the effects tested in the analysis of fertility showed significance.On the other traits, year was significant except for survival. Location was significant for pounds weaned per ewe mated and for lambs born, percent weaned and pounds weaned per ewe lambing. The main effect of the hill land was superior except for lambs born per ewe which lambed. Dam age was significant except for survival. The age effect on fertility was not tested. Otherwise pro- duction increased with age. Dam weight change during the mating season was significant for pounds weaned per ewe mated and forprolificacy. Pounds weaned increased with weight gain while prolificacy decreased. Lambing date was significant for lambs born and lambs weaned per ewe lambing. Prolificacy increased as the lambing season progressed. Location x year interaction effects on pounds of lamb weaned per ewe mated and on lambs weaned, percent weaned and pounds of lamb weaned per ewe which lambed were significant. Dam breed and dam x location interaction were significant for pounds weaned per ewe mated. The overall and hill land ranking of ewe breeds was Willamette, Suffolk, then Hampshire. The interaction re. sulted primarily from a disproportionate increase in the performanceof the Willamette ewes on the hill land. The Suffolk ewes were superior on the irrigated pasture. This suggests that a superior adaptation of Willamette ewes to hill land has resulted during their developmentand selection there. Sire x year was significant for lambs born. The inter- action effect alone, however, in no case was more than 0.10lamb so its importance is questionable. Heterosis and heterosis x location inter- action were significant for pounds weaned per ewe mated. Heterosis was 31.3% for pounds weaned per ewe mated on the valley pastureand 8.2% on the hill pasture. These results suggest that heterosis is greaterwhen conditions for the expression of a given trait aresuboptimal. Genotype x Environment Interactions in Sheep by Kathleen Steele Corum A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Master of Science Commencement June 1974 APPROVED: Redacted for privacy Assistant Professor of Animal Breeding and Genetics in charge of major Redacted for privacy Head of Department of Animal Science Redacted for privacy Dean of Graduate School Date thesis is presented Typed by Linda Peoples for Kathleen Steele Corum Acknowledgements The author expresses appreciation to Drs. W. D. Hohenboken, K. Rowe and L. Swanson for guidance and counsel in the preparation of the study program and of this thesis. Thanks are extended to Drs. Ralph Bogart and C. W. Fox for the de- sign of this experiment, and again with Dr. W. D. Hohenboken for its administration. Appreciation is shown to Mr. Millard Shelton and Mr. Lloyd Wescott for collection of the data. Thanks are extended also to Dr. Kenneth Rowe for advice and assistance in the computer analysis of this data. A special acknowledgement is made to my husband, Kell, for his encouragement, support and good humor during the thesis preparation. TABLE OF CONTENTS I. Introduction Objectives II. Review of Literature 4 III. Materials 11 Source of Experimental Animals 11 Mating Scheme 11 Environments 12 Management Practices 14 IV. Methods 16 Components of the Fertility Model 18 Components of the Model Analyzed on a Per Ewe Mated Basis....19 Components of the Model Analyzed on a Per Ewe Lambing Basis..20 V. Results and Discussion 22 Environmental Effects and Interactions 26 Breed Effects and Breed x Environment Interactions 35 Heterosis and Heterosis x Environment Interaction 42 VI. Summary and Conclusions 47 VII. Bibliography 51 VIII. Appendices A. Breed Means for Fertility 55 B. Breed Means for Ewe Production Traits 56 C. Breed/Year/Location Means 58 D. Location Means 68 69 E. Heterosis LIST OF ILLUSTRATIONS Figure Page 1 Location x Year Interaction for Lambs Weaned per Ewe 31 Lambing 2 Location x Year Interaction for Percent Weaned 32 3 Location x Year Interaction for Pounds Weaned per 33 Ewe Mated Location x Year Interaction for Pounds Weaned per 34 Ewe Lambing Breed Effects on Pounds Weaned per Ewe Mated 37 Dam x Location Interaction for Pounds Weaned per 39 Ewe Mated 7 Sire x Year Interaction for Lambs Born per EweMated 40 8 Sire x Year Interaction for Lambs Born per Ewe Lambing 41 Means of Specific Crosses for Pounds Weaned per Ewe 43 Mated 44 10 Heterosis x Location Interaction LIST OF TABLES Table Page I. Mating SchemeUsed Each Year 13 II. Least SquaresAnalysis of Variance forEwe Fertility 23 III. Least SquaresAnalyses of Variance forEwe Productivity 24 Based on EwesMated (M) IV. Least SquaresAnalyses of Variance forEwe Productivity 25 Based on EwesWhich Lambed (L) V. EnvironmentalEffects on Ewe Production Traits 27 VI. Breed Effects on Ewe Production Traits 36 GENOTYPE X ENVIRONMENT INTERACTIONS IN SHEEP I. INTRODUCTION Increases in the costs of sheep production, particularly due to rising grain prices, are resulting from increasing human consumption of grain products and the competition for grains from more efficient domes- tic species. This and the decreasing wool returns resulting from compe- tition of synthetic fibers with wool are placing increased pressure on the sheep industry to improve the efficiency of production and to put more emphasis on lamb production. Utilization of less costly by-product feeds and range lands and increasing the production of lambs are vital to the prosperity of the sheep industry. Total pounds of lamb weaned per ewe mated is the best single measure of a flock's production, consequent- ly more attention is being given to the number of lambs produced per ewe as well as to the quality of the individual lambs. There is a large amount of evidence which indicates that breed per- formance is influenced by environment in a non-additive manner. An obvious example is the suitability of Merino and Rambouillet sheep to arid climates and of Suffolk and Hampshire sheep to areas of higher rainfall. The arid climate may not provide the forage necessary for the larger, faster growing Down breeds to attain their genetic potential for growth. In the arid climate, the better suited wool breeds may actually excel in the characteristic, growth, for which the Down breeds were developed. The extent and importance of genotype x environment inter- actions needs to be determined.The relative economic suitabilities of feeds and range lands for sheep can change. With these changes, the relative merits of sheep breeds may also change. There are many breeds of sheep throughout the world. The British, for example, have developed a large number of breeds, each with a specific purpose or local adaptation. The Scots often say that the Cheviot is best adapted to grass ranges, the Blackface to heather covered hills. "However, the reported belief among shepherds in the North of England (Clarke, 1963) that the Herdwick should be grazed 'on the wet side of a fell, the Swaledale on the dry side' may be carrying the idea of local adaptation a bit far." (Carter et al., 1971) Some of this great multiplicity of breeds may be attributable to personal preference and to poor roads and transportation, but some tangible differences have developed to justify the discrimination between breeds. How many breeds are needed though? Singh et al. (1967) points out that genetic improve- ment of breeds is costly and time consuming and suggests that limited facilities be devoted to fewer, more promising breeds and that those with lower performance be discarded. The question suggested here is whether breeds can be so unequivocally ranked. The existence of genotype x environment interactions which involve a change in rank of genotypes in different environments would make the estimation of overall breed effects meaningless. The existence of economically important genotype x environment interactions could render a new dimension to genetic improvement, performance tests and selection programs. Breeds and/or mating systems would have to be selected, tested and developed in the environment of their anticipated use with 3 the expectation of poorer performance elsewhere, or alternativelybreeds and/or mating systems would have to be selected for adaptabilityunder a wide range of environments and maximumsuitability in any of the environments sacrificed. Objectives The objectives of this experiment were to evaluate theHampshire, Suffolk and Willamette breeds of sheep and to documenttheir strengths and weaknesses; to determine whether heterosis existedin crosses between these three breeds; to examine environmental effects andthe interactions between them; and to examine breed and heterosis interactionswith en- vironment in ewe production traits. The models included sire breed, dam breed, location, year, sires nested within locationswithin years, dam age, dam weight change during the mating season,lambing date, and the two-, and three-way interactions between location, year,sire breed and dam breed.